For economic and other reasons, diazo film is increasingly used for making copies of microfiche masters. Generally speaking, diazo film is first exposed and thereafter it is developed in aqueous ammonia vapor. With usage, the vapor must at least be intermittently replenished with fresh vapor. This is particularly important in connection with the recently developed micro-chambers which have physical dimensions only slightly larger than those of the film because there is only a relatively small volume of vapor which, during rates of high film throughput, becomes relatively quickly spent. Thus, in connection with micro-chambers, it is necessary to supply fresh aqueous ammonia vapor on a more or less continuing basis.
Because of their noxious stench, ammonia vapors cannot be discharged into the atmosphere unless the volume is very small. Thus, some other means for removing spent ammonia vapors must normally be devised. In the past, several approaches were employed. In a most simple arrangement, the developing chamber is defined by a pair of opposite, spaced apart platens which are heated so as to maintain the vapor temperature in the gap between them above the dew point of the vapor. The vapors, however, were allowed to escape into a housing which encapsulates the platens. The housing walls are at a lower temperature and aqueous ammonia vapor was permitted to condense thereon. By devising properly arranged guide channels, accumulating aqueous ammonia droplets could be collected in a suitably disposed drain for discharge to a waste ammonia tank or the like.
A shortcoming encountered with this approach is that the overall volume of the housing into which ammonia must be introduced is relatively large so that the ammonia consumption is correspondingly high with only a small portion of the ammonia being actually used for developing the film. Further, because of the large volume, the opening of the developer for repair, maintenance and the like releases significant amounts of ammonia vapor into the surrounding atmosphere which is undesirable. Most significantly, however, the accumulation of aqueous ammonia droplets cannot be well controlled and such droplets might from time to time contact the film being developed in the chamber. Any such contact is highly detrimental to the developing process and normally renders the film unacceptable.
In the past, attempts have also been made to withdraw the aqueous ammonia vapor from the chamber on a more or less continuing basis and to condense the ammonia outside the chamber. Although this overcomes some of the problems mentioned in the preceding paragraph, it requires the installation of relatively complicated and, therefore, costly pumps, conduits and condensers which require constant maintenance and which, unless constantly checked, may leak and release relatively large amounts of ammonia vapors to the surrounding atmosphere.
A still further prior art attempt to remove spent ammonia from the developing chamber is to place one or more condenser plates into the chamber so that aqueous ammonia vapor can condense thereon. The condensate is then withdrawn by gravity through properly arranged channels, drainage holes and the like. Again, a problem encountered with such an arrangement is the fact that the removal of the vapor from the chamber requires the formation of discreet aqueous ammonia droplets. Only after the droplets have reached a sufficient size so that they can gravitationally run off the condenser plates is it possible to remove the spent ammonia from the chamber. However, the presence of such droplets in the chamber always brings with it the danger that they be contacted by the film which, as above described, damages the film.
From the foregoing, it is apparent that up to now difficulties have been encountered in handling the aqueous ammonia in diazo film developers. Economically feasible approaches often compromised the quality of the film and could lead to excessive rejects. On the other hand, methods for handling the ammonia which did not compromise the quality of the film were relatively expensive. Thus, there is presently a need for an efficient, low cost ammonia handling system for diazo film developers which assures high quality developed diazo film.